This invention relates to a method of controlling a vehicle hydraulic brake system provided with a pump for producing brake hydraulic pressure.
In recent years, in order to realize sophisticated vehicle behavior control and a light brake operation feeling, as described e.g. in patent publication 2590825, a vehicle hydraulic brake system is employed in which a pump as a hydraulic pressure source for producing brake hydraulic pressure is provided and a motor for driving the pump is actuated based on a detection signal of a brake operating force detecting means for detecting the operating force of a brake operating member.
Among such pump-driven type brake systems, there are ones in which a master cylinder for producing hydraulic pressure corresponding to the operating force applied to the brake operating member is in communication with wheel cylinders through an on-off valve by way of a so-called master cylinder passage, and if the pump is not operating normally, the hydraulic pressure in the master cylinder is transmitted as brake hydraulic pressure by opening the on-off valve to provide a failsafe function.
For such pump-driven type brake systems, a method of controlling the driving force for the pump-driving motor with the brake hydraulic pressure corresponding to the brake operating force as detected by the brake operating force detecting means as a target value is often employed. For such controls of the motor driving force, PID control is ordinarily employed.
In the control method of such a pump-driven type vehicle hydraulic brake system, there is a delay in response after the brake operating force has been detected by the brake operating force detecting means until the pump-driving motor is actuated, so that rise of the brake hydraulic pressure is slow. Thus, in the initial period of operation of the brake operating member, a large difference in hydraulic pressure is produced between the control target value of the brake hydraulic pressure and the actual brake hydraulic pressure.
Thus, in the above-described conventional control method, if the control output of the motor driving force is increased corresponding to the hydraulic pressure difference, the brake hydraulic pressure in the wheel cylinders pulsates due to brake fluid discharged from the pump, so that no smooth control is possible. Also, if the control gain is reduced to suppress such a pulsation of the brake hydraulic pressure, a speed at which brake hydraulic pressure follows the target pressure slows down, so that the driver feels a delay in the braking effect. During abrupt braking, it is possible that the braking effect will not appear in time.
An object of this invention is to provide a control method of a pump-driven type vehicle hydraulic brake system which can suppress pulsation of brake hydraulic pressure and makes it possible to accurately and quickly apply brake hydraulic pressure.
According to this invention, there is provided a method of controlling a vehicle hydraulic brake system comprising a wheel cylinder, a pump for producing brake hydraulic pressure by supplying brake fluid into the wheel cylinder, a motor for driving the pump, a fluid passage for bringing the pump and the wheel cylinder into communication with each other, a brake hydraulic pressure detecting means for detecting the brake hydraulic pressure in the wheel cylinder, a brake operating member, and a brake operating force detecting means for detecting the operating force applied to the brake operating member, and adapted to detect the brake operating force by the brake operating force detecting means and control the driving force of the motor with the brake hydraulic pressure corresponding to the detected brake operating force used as a target value, characterized in that an equation showing the relation between the rising speed of the brake operating force and the driving force of the motor required to cause the brake hydraulic pressure to follow the brake operating force is determined beforehand, and the driving force of the motor is preset from the rising speed of the detected brake operating force by use of the equation, and the driving force of the motor is controlled so as to decrease the hydraulic pressure difference between a target brake hydraulic pressure and the brake hydraulic pressure which is estimated to rise by the preset driving force or the actual brake hydraulic pressure that has been increased by the preset driving force of the motor.
That is to say, by determining an equation showing the relation between the rising speed of the brake operating force and the required driving force of the motor beforehand, setting the driving force of the motor from the rising speed of the detected brake operating force by use of the equation, controlling the driving force of the motor to decrease the hydraulic pressure difference between the estimated value or actual value of the brake hydraulic pressure to bring the brake hydraulic pressure substantially close to the target value with the set driving force, and only for the remaining hydraulic pressure difference, controlling the motor driving force with a small control output, it is possible to quickly and smoothly cause the brake bydraulic pressure to follow the target value.
This control method for the vehicle hydraulic brake system can also be employed for a brake system in which a master cylinder for producing hydraulic pressure corresponding to the operating force applied to the brake operating member is provided, and a master cylinder passage for communicating the master cylinder with the wheel cylinder through an on-off valve is provided to transmit the hydraulic pressure produced in the master cylinder by selectively opening and closing the on-off valve in the master cylinder passage.
By adding the value of the brake hydraulic pressure itself to the equation between the rising speed of the brake operating force and the driving force of the motor as a parameter, since the required driving force of the motor slightly changes with the level of the brake hydraulic pressure itself, it is possible to increase the accuracy of control for bringing the brake hydraulic pressure close to the target value with the set driving force.
If a master cylinder for producing hydraulic pressure corresponding to the operating force applied to the brake operating member is provided, means for detecting the hydraulic pressure produced in the master cylinder is provided, and the hydraulic pressure in the master cylinder detected by the master cylinder hydraulic pressure detecting means can be used as a brake operating force in the control.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: